Alkoxides silicate

A critical provision needs to be emphasized in this discussion on stability of lignin-silicate structures, however. The discussion on alkoxide-silicate bond stability was pie ced by "in isolation", meaning a single bond in solution or a swollen gel. If the alkoxide-siUcate bond is formed in a sample which ultimately loses all water, the sensitivity ofthe carbon-oxygen-silicon bond to hydrolysis, while it still exists, is irrelevant because no water will everreach that bond to lyse and separate it Once a collapsed, hydrophobic aggregate of silicate and lignin-silicate bonds forms, the capacity of... 

Very recently, Wilkes and co-workers 330,331) have reported the preparation and characterization of hybrid materials, which they named as ceramers . Ceramers were synthesized through the incorporation of polymeric or oligomeric PDMS into silicate glasses by a sol-gel process as shown in Reaction Scheme XXIV. During these reactions the variables such as the type of the alkoxide used, amount of water added, the pH value of the reaction system, and the reaction temperature, were carefully monitored. 

In other studies, the combination of alkoxides and chlorides, or alkoxides and amides without oxidant have been used to deposit hafnium silicate thin films by ALD [3,7],... 

The use of alkoxides for fabrication of silica materials has some advantages that will be discussed later. They serve as a precursor a silicic acid is generated in the course of their hydrolysis that thereafter enters into condensation reactions (1). The main processes may be presented by Scheme 3.1. 

The sol-gel technology, based on various alkoxides, allows production of classical silica glasses, as well as multicomponent materials, merging silicates with titanates, borates and a variety of other oxides (Zn, La, Al, Li, B, K, etc.). The alkoxide gel method can be also used for production of certain non-silicate oxide glass-like materials (e.g., ZrCV, etc.)25. 

Stober A process for making metal oxides in the form of small spheres of uniform diameter by the controlled hydrolysis of metal alkoxides. First used in 1968 to make silica spheres from alkyl silicates. The products can be used to make high quality oxide ceramics. See also Sol-Gel. 

A number of reagents containing oxide components are used in zeolite manufacture [19]. Silica is provided by addihon of sodium or other alkali silicate solutions, precipitated, colloidal, or fumed silica, or tetraalkylorthosihcate (alkyl = methyl, ethyl) and certain mineral silicates such as clays and kaolin. Alumina is provided as sodium aluminate, aluminum sulfate soluhon, hydrous aluminum oxides such as pseudo boehmite, aluminum nitrate, or aluminum alkoxides. Additional alkali is added as hydroxide or as halide salts, while organic amines and/or... 

The metathesis reactions, where MOR or M(OR)2 are used as alkaline agents in nonaqueous medias, provide efficient approaches to high-purity samples of MHal [1000], M2S, and M2Sn [805, 806, 1009, 1036], MHSe [1566], silicates [1593], peroxides, oxides [77], and so on. The most important, however, is played by the metathesis of M OR with MHal , which is one of the major routes to the alkoxides of multivalent metals (see Section 2.5). 

Silica nanoparticles are commonly prepared by polymerization of appropriate precursors such as silicates, silicon alkoxides, or chlorides (Fig. 11.2).2 Besides the industrial methods, which rely mainly on condensation of sodium silicate in water induced by sodium removal through ion exchange, three different synthetic methods are currently used in research labs to prepare silica nanoparticles loaded with organic molecules. In the first method, proposed by Kolbe in 1956s and developed by Stober and coworkers in the late 1960s,6 the particles are formed via hydrolysis and... 

Another route for the production of materials involves the reaction of hydrolysis-condensation of metal alkoxides with water. We study here the important case of amorphous silica synthesis. In this case [38,39,44], silicic acid is first produced by the hydrolysis of a silicon alkoxide, formally a silicic acid ether. The silicic acids consequently formed can either undergo self-condensation, or condensation with the alkoxide. The global reaction continues as a condensation polymerization to form high molecular weight polysilicates. These polysilicates then connect together to form a network, whose pores are filled with solvent molecules, that is, a gel is formed [45],... 

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